The invention relates to a method for operating a chemical and/or physical process, e.g a fluid bed reaction, and especially deals with the injection of fluids, such as gases, liquids and/or suspensions in a controlled typically uniform way. More in detail, the chemical and/or physical processes are carried out within a vessel containing a fluid or fluidized medium, which medium can be a gas and/or a liquid, optionally in combination with solid particles. The fluids are injected using an injection device consisting of tubes or channels that are connected in a hierarchical fashion so that the fluid entering a first channel is divided into channels of the same or different diameter and length, each or some of which are further divided into channels of the same or different diameter and length, and so on. The is injection system can also comprise combinations of such tree-like or fractal-like elements, embedded in a plane (two-dimensional) or in space (three-dimensional).
Multiphase reactors or multiphase contacting devices, are commonly applied in process industry In such processes two or more fluids have to be brought into contact with each other to efficiently transfer one or more components from one phase into another phase, where the reaction or contacting process occurs. This is in particular so for transport limited processes, of which there are many in industrial practice.
The invention can be used for gas/solid fluidized bed, gas/liquid and other processes. A typical application is the reduction and uniformization or otherwise control of bubble sizes to optimize the operation of fluidized bed, slurry and gas/liquid reactors The embodiments of the present invention will depend upon the nature of the fluids and the application.
An important example is a fluidized bed reactor, where gas is injected through a distributor plate in the bottom of a vessel to fluidize a bed of solid particles that are to react with the gas or catalyze a chemical reaction between gas molecules, Gas bubbles grow from the bottom to the top of the bed as a result of the pressure difference-over the bed, simply because of the thermodynamics. The movement of the fluidized solid particles and the bubbles is turbulent, chaotic, and strongly dependent on the operating conditions.
Fluidized bed reactors are of considerable economic importance. An example of a large scale process that is preferably carried out as a fluidized bed process is the Fischer-Tropsch synthesis of liquid fuel from synthesis gas, which can be obtained by steam-oxygen gasification of coal or other hydrocarbons. This process involves the contacting of the gas stream with solid catalyst particles to produce the fuel: EQU aH.sub.2 +bCO=C.sub.x H.sub.y +zH.sub.2 O
Another important example in which similar problems occur is a gas/liquid process carried out in a bubble column or stirred tank reactor The gas moves up from a distributor through a reactor vessel. The movement of the bubbles is again extremely complex. Typically, the shape and size of the bubbles cannot be or is hardly controlled and bubbles coalesce and grow as a result of the pressure difference between the top and the bottom of the reactor. A mixing device and fixed internals may be installed inside the vessel to improve the mixing by increasing the turbulence in the bed. Similar complex hydrodynamics exist for other processes in which several fluids or fluidized media are contacted to react or catalyze reactions.
To optimize the reaction process, the interfacial area between the fluid phases should be maximized or otherwise controlled. With the presently used reactor systems or physical contacting devices, this forms a serious problem, especially because the hydrodynamics, as described above, are so complex.
Mixers can be used to increase turbulence and contacting, but they consume costly energy. In other cases, such as gas/solid fluidized beds, mixers may not be used. In addition, mechanical problems arise when mixing devices are employed.
Homogenization, i.e., achieving equal conditions at every point in the reactor vessel, is difficult to achieve. Imposing particular concentration or partial pressure profiles is even more difficult or for most reaction systems impossible The existence of dead volumes, where no or much less reaction occurs, because of decreased local flow, is often inevitable.
Another problem in current realizations of such multiphase reactors and other processes involving several fluids or fluidized media that need to be contacted is `scaling up` of these devices. A process is usually first investigated on a smaller scale, e.g. on lab scale, bench-scale or pilot scale, and then needs to be scaled up to the typically much larger industrial scale. Rules to scale up multiphase processes are typically empirical or at least semi-empirical and the errors are very large, because the processes are influenced by the hydrodynamics. With the present methods, it is a serious challenge to maintain similar hydrodynamics during scale up from the small to the large scale, In most cases, this is even impossible.
Whenever in this specification and the appended claims reference is made to a `vessel` it is to be understood that this refers to a container for fluids and optionally particles, in which optionally provisions are made to feed additional fluids and/or particles, and optionally provisions are made to remove fluids and/or particles. Preferably such a vessel is operated in a continuous process. The examples of processes mentioned above, are all carried out in vessels.
In the prior art several publications are known which address at least part of the above mentioned problems.
In U.S. Pat. No. 4,537,217 a fluid distributor is disclosed having a distribution surface with a plurality of uniformly spaced distribution openings, which is particularly suitable for application in chromatography.
U.S. Pat. No. 4,999,102 discloses a liquid distributor for distributing and/or collecting a liquid in large scale industrial processes, such as absorbers or desorbers.
U.S. Pat. No. 5,354,460 discloses a fluid transfer system for obtaining uniform liquid distribution in industrial scale fluid transfer systems which accommodate plug flow operations.
All of theme publications relate to the uniform is distribution or collection of a liquid by means of a planar device which stretches out horizontally. The devices described in these prior art documents are placed at the inlet or outlet of the corresponding unit-operation. Each point in the plane would be reached, were the constructions described in these documents continued ad infinitum. At the outlets, the liquid pours out or is collected in a uniform way; typical applications are in chromatography.
Finally, Kearney (in: Fractals in Engineering, INRIA Proceedings, Jun. 25-27, 1997, Arcachon, France) describes a three-dimensional mixing unit, which consists of a recursive structure of pipes. This structure is suitable for emulating turbulence using laminar flows.
The structures disclosed in above mentioned patents are not suitable or optimal for controlling three-dimensionally local parameters such as pressure and flowrates for improved operation of chemical and/or physical processes in vessels, such as described hereinbefore. Moreover, none of these documents is directed to multiphase processes, nor to scaling up such processes.